Methods for detecting an electric field vector of a terahertz wave include, roughly, (A) methods where components in two axial directions orthogonal to each other (e.g. X axis and Y axis) are detected separately and synthesized thereafter and (B) methods where an electric field vector is directly detected. As one of the methods of (A), for example in non-patent literature 1 (M. B. Byrne, M. U. Shaukat, J. E. Cunningham, E. H. Linfield, and A. G. Davies, “Simultaneous measurement of orthogonal components of polarization in a free-space propagating terahertz signal using electro-optic detection, “Appl. Phys. Lett. Vol. 98, p. 151104 (2011)), a terahertz wave is divided into polarized components in two orthogonal axial directions and these polarized components are detected by two detection systems. Thereafter, the obtained two detection results are synthesized to detect an electric field vector of the terahertz wave.
Also, in non-patent literature 2 (N. C. J. van der Valk, W. A. M. van der Marel, and P. C. M. Planken, “Terahertz polarization imaging,” Opt. Lett. Vol. 30, p. 2802 (2005)), polarization of probe light is caused to be circular polarization and a (111) crystal is used where a (111) surface of an optical isotropic medium is cut out as an electro-optic crystal for detection of a terahertz wave. In this method, the probe light having probed the terahertz wave is divided and detected by two detection systems for separately measuring terahertz waves in two orthogonal axial directions. Thereafter, the obtained two detection results are synthesized to detect an electric field vector of the terahertz wave.
Meanwhile, as one of the methods of (B), for example in non-patent literature 3 (N. Yasumatsu and S. Watanabe, “Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor,” Rev. Sci. Instrum. Vol. 83, p. 023104 (2012)), an electric field vector of a terahertz wave is detected based on a shift in detection signals of probe light when an electro-optic crystal for detection of a terahertz wave is rotated. Furthermore, in non-patent literature 4 (N. Nemoto, T. Higuchi, N. Kanda, K. Konishi, and M. Kuwata-Gonokami, “Highly precise and accurate terahertz polarization measurements based on electro-optic sampling with polarization modulation of probe pulse,” Opt. Express vol. 22, p. 17915 (2014)), a (111) crystal is used where a (111) surface of an optical isotropic medium is cut out as an electro-optic crystal for detection of a terahertz wave and a polarization direction of probe light is rotated while linear polarization is maintained. An electric field vector of the terahertz wave is detected from a shift in detection signals associated with a shift in the polarization direction of the probe light.
In non-patent literature 5 (N. Yasumatsu, A. Kasatani, K. Oguchi, and S. Watanabe, “High-speed terahertz time-domain polarimeter based on an electro-optic modulation technique,” Appl. Phys. Express vol. 7, p. 092401 (2014)), a (111) crystal is used where a (111) surface of an optical isotropic medium is cut out as an electro-optic crystal for detection of a terahertz wave and polarization of probe light is caused to be circular polarization, thereby probing the terahertz wave. The probe light having probed the terahertz wave is modulated by an electrooptical modulator and then an electric field vector of the terahertz wave is detected based on a shift in the modulated signals.